Signal receiver



M. G. CROSBY 2,230,212

SIGNAL RECEIVER Original Filed June 20, 1932 6 Sheets-Sheet 1 ln QW' INVENTOR. RAY G. CROSBY www ATTORNEY Jan. 28, 1941.

Jan. 28, 1941. M. G. cRosBY SIGNAL RECEIVER original Filed June 2o, 1932 6 Sheets-Sheet 2 HHM.

Jam 28, 1941! M. G. cRosBY SIGNAL RECEIVER 4(5 Sheets-Sheet 3 Original Filed June 20, 1932 C ORRECT/N FOR FM RECE/VER kblkbb REcE/V/N f PM WA VES AUD/0 FREQUENCY U AuD/o FREQUENCY FREQ,

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Jan. 28, 1941. M. G. CROSBY 2,230,212

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Jan. 28, 1941. M Q CRQSBY 2,230,22

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M. G. CROSBY SIGNAL RECEIVER Original Filed June 20, 1932 6 Sheets-Sheet 6 INVENTOR.

MURRAY 6. CROSBY WKK/WM.

ATTORNEY.

Patented Jan. 28, 1941 SIGNAL RECEEVER Murray G. Crosby, Riverhead, N. Y., asslgnor to Radio Corporation of America, a corporation o! Delaware Original application .lune gi), 1932, Serial No.

Divided and this application March 9, 1940, Serial No. 328,077

22 Claims.

This is a division of my copending applicatio Serial No. 618,154, filed June 20, 1932.

My present invention relates to frequency and phase modulation systems and apparatus. Objects of my invention are broadly to provide lmproved arrangements for receiving phase and frequency modulated waves; to provide systems for adapting frequency modulation apparatus to the reception of phase modulatedrwaves or amplitude modulated Waves, and to lprovide circuits generally useful for phase and frequency modulated waves. Other objects as Well as advantages iiowing from my invention will appear as the more detailed description thereof proceeds.

in the drawings, Fig. l shows diagrammatically a receiver by means of which frequency and phase modulated signals may 'De demodulated;

Figs. 2, 3 and 3a, show modications of the arrangement oi Fig. l;

Figs. 4 and 5 are curves explanatory ci the operation of Figs. i, 2 and 3 when receiving phase modulated waves.

Figs. 6, 6a, '7, 7a and 8 illustrate iiIter circuits which may be included in the :frequency modulated signal receivers of the prior ilgures to adapt them to eilcient reception of phase modulated signals;

Figs. 9 and 9a, are conversion systems utilizing both frequency and phase modulation apparatus;

Fig. l0 shows diagrammatically how the correction circuits ci Figs. 6, 7, 7a, 8, 9 and 9a may be incorporated with the frequency modulation receivers of Figs. 1, 2, 3 and 3a; l

Figs. il. and lla show diagrammatically other applications of the present invention.

The operation oi all of the receivers disclosed in Figs. l, 2, 3 and 3a to receive frequency modulated signals depends upon the fact that the electrical length of a filter or a transmission line,

l which consists of a series of sections composed long for a. certain predetermined frequency, at.

a higher frequency the electrical length Will be greater and at a lower frequency the electrical length of the line will be less. The fact that (Cl. Z50- 20) 'this electrical letngth does change with frequency makes the phase at the output ci the line change with respect to that of the input of the line if the frequency .of the signal transmitted by the line is varied. Consequently, ii the signal impressed on the input of the line is combined with the signal at the output of the line, an adjustment oi the line may he made so that the phase diierence between the voltage of the signal impressed on the input ci the line and the voltage cf the signal appearing on the output ci? the lin-e increases as the degree of frequency modulation is increased. This phase difference will cause a variation in the amplitude of the resultant ci the combined voltages so that an amplitude modulation resultant is form-ed, which amplitude modulation is truly characteristic ci the frequency modulation ci the original signal. in accordance with this inven-I tion, this amplitude modulation component is then detected or rectified,

En particular, in the receiver ci. Fig. i, the irequency modulated energy appearing in lines t and t in the output ofi the hetercdyning and amplifying unit is fed directly through couu pling tube .e to the combining transformer T.y

Simultaneously energy from i appearing in lines il and is .ted hy Way ci lines i@ to transformer if? and to the transmission line L. lead it, connected to a mov/able point l? on the line L,

transfers energy in the proper phase to the potentiometer P2, from whence the energy is supplied to the coupling tube B. The output energy from the line L, adjusted to the proper phase by means of the sliding tap 2li, P, or similar means, is fed through the coupling tube B to the comhining transformer T. The above transformer T, therefore, is energized by energy from A and from B.

ln operation, asthe modulating signal changes the frequency of the carrier, the energy appearing in tube B and in particular in the output circuit ythereof, changes more rapidly in phase or in frequency than that from tube A. These re1- ative changes in phase of the energies from the two coupling tubes results in a change in amplitude of the combined energy in the primarywinding I4 of transformer T. This amplitude change or modulation vis impressed on the input circuit of detector tube C and the demodulatd signal appears in the output circuit thereof, from whence it may be utilized. When used for rep ceving phase modulated'waves'a 'correcting circuit CC is added. This correcting circuit has the characteristic shown in Fig. 4, as will be explained more fully later. Y

While this receiver of Fig. 1 has -been illustrated as. having a damped transmission line, it will be understood that in this receiver the transmission line L may be undamped, or open citcuited at the end. In this case, the tap 20, P is moved to a point on the line where the reilected wave cancels the incident wave. The operation of this modied receiver will be apparent from the description of the receiver of Fig. 3 which will be given later.

In the receiver of Fig. 2, use is made of the fact that when the line L, made up of series inductance` and shunt capacity C. is open or shortcircuited at the far end, a reection of signal energy transmitted by the line Lv occurs along the line. The combinationof this reflected energy with the incident energy results in combined energy, the amplitude of which varies. That is, when the signal frequency is changed with signal modulation a phase difference between the incident and reected waves of line L is caused such that their resultant amplitude changes. Consequently, amplitude modulation of the energy in the line at different points therealong is effected by permitting far end reections. By obtaining the output froml the line L at two different points Pz, P4 by way of leads 35, 31, connected at points such that at one point the incident and reected waves combine to increase the resultant, While at the other point the two waves combine to decrease the resultant, two separate waves with modulation envelopes 180 out of phase may be obtained. These two waves may be, and are, applied as shown to the differential detectors A and B by way of leads 35 and 31, respectively.

The detected output appearing on the anode 42 of detector.A is 180 out of phase with respect to the detected output appearing on the anode Q3 of detector tube B. This necessitates the use of a push-pull transformer T connected to the outputs of tubes A and B. The demodulated signal may be utilized in` circuit 41. Where this receiver is used to receive amplitude modulated signals the output electrodes 42 and 43 of demodulators A and B, respectively, must be connected in parallel relation so that the amplitude changes add rather than oppose each other.

The receiver of Fig. 2 has an important advantage Which is that the diiferential detectors employed in the output produce a cancellation of distortion resulting from ysquare law detection and consequently a reduction of noise appearing with the signal in the output circuit.

'I'he transmission line L of the receiver of Fig. 2 may be undamped or open-ended, or shortcircuited at its far end, or end away from its input terminals.

When the receivers of Figs. 2, 3 and 3a are used to receive phase modulated Waves, switch 46 is thrown to its frequency modulation position, i. e.

so that the detector outputs are combined in phase opposition. Also, a correcting circuit CC,

which will be' described in detail more fully hereinafter, is added. Briefly, the correcting circuit has a characteristic of output of frequency as shown in Fig. 4. Incidentally, for a more detailed description of the receivers shown in Figs. 1, 2, 3 and 3a, reference is made to my parent application Serial No. 618,154, -filed June 20, 1932.

In Fig. 3a, the grids 34, 36 of differential detectors C and D are fed, by means of a transformer T2, cophasally with signal energy from the output of the unitw. Lines 3 and Sjalso'feed l detectors C and D in phase opposition with frequency or phase modulated energy by way .of transformer T1, the input of which is connected with the output of the coupling tube A. Tube A in turn has its input circuit connected to a point I0 on transmissionline L. The resultant amplitude modulation components fed to the detectors C and D are effectively out of phase. i

By means of the push-pull output transformer T4. connected with the anode circuits of C and D respectively, the rectified energies appearing in the output circuits of C and D are combined in proper phase when frequency modulation is received. i

The receiver illustrated in Fig. 3a may be readily altered to receive either frequency modulated or amplitude modulated signals by merely connecting the outputs of tubes C and D in pushpull'relation for frequency modulated waves, or in parallel relation for amplitudemodulated waves. This is accomplished by switch 46 While the receiver'of Fig. 3a has been illustrated as utilizing a damped transmission line, it will be understood that in this receiver, the

transmission Vline L may be undamped, that is,V open-circuited or short-cirouited. In thisy un-l damped case the tap l0 isy adjusted to a point on the line where the reflected wave cancels the incident Wave at the carrier frequency.

`Volume controls, coupling tubes, and additional amplifiers may be added to the receivers in appropriate places. Since .the use of such elements will be obvious to those skilled' in the art, and for the sake of simplicity, such elements have been omitted from the present disclosure.

The receivers of Figs. 2, 3 and 3a may, of course, be operated with one detector tube switched oil'.

The receivers described above may, in accordance with the present invention, be used for the reception of phase modulation waves.. As already explained to some extent, this is accomplished by adjusting the circuits for frequency modulation as described above and using a correcting filter or circuit at the receiver whichhas its output voltages inversely proportional to its input frequency so that its characteristic is as shown in Fig. 4, wherein audio frequency impressed on the input terminals of the correction circuit is plotted against voltage output.

When phase modulated signals are received on a frequency modulation receiver, the signal out- Jput of the frequency modulated receiver 'varies in amplitude directly with the frequency 'ofv the signal at the input of the frequency modulated signal receiver. Consequently, Athe audio frequency output of this receiver would be distorted and would be lacking in low frequencies. The.

output of the receiver instead of being the same for all audio frequencies, as shown by the dotted line of Fig.' 5, would be directly proportional to the frequency of the signals impressed. on the input lof the receiver, as shown by the full'line of Fig. 5. In order to compensate for this dis'- tortion of the signal frequency when phase modulated signals are received on a frequency modulated signal receiver, a lter circuit or correction.

nals. The combination of the effect of a lter circuit or correction circuit having characteristics as illustrated by Fig. 4 with the effect yof the inherent characteristics of a frequency modu- 5 lated receiver on phase modulated signals gives an over-all characteristic such as the dotted line of Fig. 5, which is a true reproduction of the sig- A nal wave applied as phase modulation to the carrier at the transmitter.

This correction filter or circuit CC is used with the receiver and is connected at a point following the detector, as shown in Figs. l. 2, 3 and 3a..

- Various forms of lter or correction circuits, which will ail'ect the signal frequencies passed therethrough in such a manner as to make the amplitude of the signals at the output thereof inversely proportional to the frequency of the signals applied to the input, may be used. Several preferred forms of correction circuits, will now be described.

In Fig. 6. phase modulated waves picked up on the antenna are translated into signal waves by the frequency modulation receiver FMR such as described in Figs. 1, 2, 3, or 3a. The correcting circuit CC is added to reproduce an undistorted signal in jack J. That is, in Fig. 6 the signal frequencies to be corrected are applied to the primary winding of a transformer 5i! and are impressed from thev secondary winding of said transformer to the input electrodes 52, 5ft cfa thermionic tube 5| to energize the same. The control electrode 52 of tube 5| is maintained at the desired operating potential by means of a biasing source 55. The anode electrode 55 of tube 5| is connected through a parallel circuit comprising a resistance 51 and capacity 58 to the cathode 54 by way of a high potential charging source 58. The low frequencies of the signal potentials 'are emphasized by means 'of the ca- 40 pacity 58 connected across the resistor 51. The impedance of this resistance 51 and capacity 5B in parallel is high at the lower signal frequencies and low at the higher signal frequencies. The

amplincation factor ofv the tube 5|, which deprimary winding B3 of the transformer winding 55 5I. The corrected signal frequencies may be utilized from the secondary winding 65 of the transformer 53. In order to operate 52 at the desired point on its characteristic curve, biasing potential is supplied from the source 56 by way s0 of resistance 51 to the control electrode 5| of tube 82.

If the single distortion or correction tube 5| does not effect sumcient distortion or correction of the signal frequencies passed therethrough,

65 'a second tube, connected in circuit and operated similar to tube 5|, may be connected in cascade with 5| to apply more distortion or corrective effect to the signal. This arrangement is shown in Fig. 6a.

70 In Fig. 7, the signals to be 4corrected are impressed on the input winding of a transformer 50 and utilized from the secondary winding 85 of transformer 5l in the same manner as in the arrangement of Fig. 6. In Fig. 7. however, no

7s amplifier is shown connected with the correction tube 5|. although it is understood that the corrected signals can be further amplified, if necessary, by connecting the output of tube 5| with the input of `a thermionic amplifier. The secondary winding of the transformer 50 is con- 5 nected in parallel with the potentiometer resistance 'I0 in order that the'desired signal amplitude may be impressed on the input electrode 52 by way of the tap In this arrangement the resistance Rn is of such a high impedance to the i0 signal current as compared to the impedance of the capacity Cz to the signal current that the current passed through the circuitsRa C: is governed mainly by the resistance of Rz. This makes the current through the circuit elements 15y C2, Ra constant with frequency so that the voitage across C.; will be inversely proportional to the frequency of the applied signal due to the fact that thev impedance of the condenser C2 varies inversely as the frequency of the signals 20 applied across the terminals thereof vary. The potentials appearing at the terminals of Ca are impressed on the input electrodes 52, 5t of correction tube 5|.

In. the arrangement shown in Fig. 'la correction 29 is applied to the signal in the same manner in which correction is applied thereto by the arrangement shown in Fig. 1. However, in Fig. 7c,

a second tube 5i is added for the purpose of varying the amount of distortion or corrective 30 edect applied to the signal waves relayed therethrough. When .tube 5i is switched 0H full correction will be' obtained by means of the tube 5i in the sam'e manner in which correction'is obtained in the arrangement of Fig. 7. With the 35 tube 5i turned on signal potentials, the amplitude of which maybe determined by the tap iii', will be applied from the parallel resistance i0' to the terminals of the resistance Ri by way of resistance Rs. The resistances R3, R4 will affect a0 all ofthe frequencies of the signal impressed thereon in like manner so that no corrective effect will be applied to the signal appearing on the input electrodes 52 of the tube 5i. Consequently, the oscillations at signal frequency, appearing on the anode 56 of tube 5i and applied therefrom to the transformer 5s, will be the same for all frequencies-and will represent in a normal manner the signal potentials applied at the input of the correction circuit. By moving the taps 1| and 1|' along the resistances iii and 10', the amount of corrected signal and uncorrected signal reaching the output circuit 63 can be ad-l iusted to give the desired characteristic to the signal frequency in the output circuit, which characteristic may beA somewhere between full correction of the signal and no correction.

This type of correction circuit is useful where it is desired that the transmitter radiate a cornbined frequency and phase modulatedsignal or 6 a cross between frequency `and phase modulated signal. Furthermore, such an arrangement is especially desirable where a correction circuit of this type isv used in the signal amplifier circuits 65 of the transmitter and a second correction circuit of this type is used subsequent to the detector in the receiver receiving signals from said trans-l mitter.

In the correcting circuit shown in Fig. 8, as in the prior arrangements, the signals to be cnrrected are impressed on the transformer 50 and the corrected signals are utilized from the transformer 54. In this arrangement, however, a different means is provided for emphasizingthe lower frequencies of the signal. The value of the inductance XL in series with the control electrode is so chosen that its impedance to th signal frequency is high as compared to the impedance of the resistance R5 to the signal frequencies. 'I'he inductance XL then is' the governing factor of the circuit and determines the intensity of the current passed through the circuits XL, R5. Since the inductance XL. o ffers a higher impedlance to the higher frequencies than to the lower frequencies, the current passing through the inductance XL` will be inversely proportional to the frequency of the impressed signals. Consequently, the voltages at signal frequency, appearing across the yresistance R5, which are fed to the control electrode 52 of tube 5|, Will be inversely proportional to the frequency of the impressed signals.

In Figs. 9 and 9a has been shown an arrangement in which, by means of a novel circuit, a corrective effect, which is the converse of the manner in which phase modulated signals are distorted in a frequency modulation receiver, is applied to the signals. The distortion of the signa-l wave discussed hereinbefore is created by virtue of the fact that that phasemodulated waves are being received on a frequency modulated signal receiver. On the other hand, if a circuit is set up which receives frequency modulation on a phase modulation receiver, -a distortion is created which is the inverse of the undesired distortion obtained when phase modulation is received on a frequency modulation receiver. Obviously, if the phase modulated signal is passed through these circuits in sequence, the distortion effects, which are the inverse of each other, will add or cooperate to give a resultant signal which isl truly representative of the initial signal to be worked with. This might seem like a devious route to follow to receive phase modulation. Actually, it is not, however, and is, on the contrary, a Iconvenient manner to receive phase modulated signals under certain conditions. The phase modulated signals are rst received ona frequency modulated receiver, then converted by means of a local modulating means (transmitter) to frequency modulation, and received on a phase modulation receiver as shown in Fig. 9.

The logical assumption may be that, since a phase modulated signal receiver is used in this correction circuit, the phase modulations should be received directly on that unit. However, there are reasons for following the present course. First, the received signal output from phase modulated signals received on a frequency receiver, including correcting means as illustrated in Figs. 6, 7, 7a and 8, is di'erent from that received directly on a phase modulation receiver.

with respect to interference, fading, and ytuning; characteristics. Consequently, a corrected frequency modulation receiver (receiving phasfe modulated signals) will feed a certain circuit more suitably than a phase modulation receiver the phase modulated signal picked up by the antenna to the input terminals of a transformer 50. The secondary winding of transformer 50 is connected to the control electrode 90 of an oscil lation generator 9| of the dynatron type. The anode 92 is connected with an oscillatory circuit 93 in which oscillations at high frequency are developed by producing a negative resistance effect in the anode cathode circuit, as disclosed more-in detail in United States application Ser. No. 808,383, filed April 30, 1932, now Patent No. 2,085,739,- issued July 6, 1937. The high frequencies generated by the dynatron oscillator are modulated in frequency, as disclosed more in detail in the above identified application. The modulated oscillations are impressed from the circuit 93 on to a winding 94, and from winding I in opposition to the control electrodes 95 and 96 of thermionic differential detectors 98 and |00 of a phase modulation receiver. The anodes |0| and |02 of differential detectors 98 and |00 are connected in series through resistances 0 and Il i, as shown. Charging potential for the anodes is supplied from a source |03 connected between the terminals of resistances I`|0 and and the cathodes of tubes 98 and |00. The different currents resulting from the signal frequencies impressed oppositely to the control electrodes of tubes 98 and |00 flow in the resistances ||0 and These different currents are applied from the high potential terminals of resistances ||0 and lll .to the input terminals of a radio filter circuit comprising series inductances I, I' and parallel condensers C4 connected as indicated. After passing through the filter circuits I, I', C4 the different currents iiow through resistances R5, Re to the control electrode |05 and cathode |06 of a second dynatron oscillation generator |08. Capacities C5 are 'connected between the terminals of the resistances Rs, Re and ground. These resistances and capacities regulate and determine the time constant of the circuit interposed between the differential resistors ||0, ||I

`and the input electrodes of the oscillation genera'tor |08 to regulate the sensitivity and rapidity of the control effect of .the different currents on the oscillator |08.

A source |09 supplies direct vcurrent biasing potential to the grid electrode of tube |08. The differential currents from resistances ||0 and ||I are superposed on this direct current potential. The output circuit ||2 of the dynatron oscillation generator and modulator |08 is coupled through a link circuit I3 with a transformer H4, the secquency control means for the supplemental modulator and generator |08 is, in many respects, similar to the automatic frequency control device disclosed in' United States Appln.`Ser. No. 616,803, led June 13, 1932, now Patent #2,065,565, issued on Dec. 29, 1936.

.The detected signals appearing in the anodes of differential detectors 90 and |00 are applied by way of coupling condensers ||6 and H1 to the terminals of series resistances ||8, H0 and from the terminals of said resistances to the control electrodes of a pair of amplier tubes |20 and |2| having their anodes connected through assuma t the primary` winding 63' of a .transformer I4'. This phase modulation receiver, including the differential detectors 98 and |00, the frequency control means Hi8, and the repeaters IZB and I2i, impart to the modulated signals from frequency modulated dynatron 90, a distortion which is the converse oi the distortion given to the initially received phase modulated signal by the frequency modulation receiver FMR. 'I'he two distortion effects add to provide in the output of transformer 84 a signal which is truly representative of the signal impressed on the original phase modulated wave. The corrected signal frequencies may be utilized from the secondary winding of this transformer.

Any one of the correction circuits illustrated in Figs. 6, 7, 7a, 8, 9, and 9a, may be utilized with f the frequency modulated receivers of Figavl, 2, 3

and 3a, as indicated in Fig. 10, in which i is the aerial system, 2 is asigna] amplifier of any type, and 80 indicates any one oi the phase or irequency or amplitude receivers of Figs. l, 2, 3 and 3a connected to 2 by way of leads 3 and d. The correction circuits of Figs. 6.,'7, 7a, 8, 9 and 9a; may be incorporated in the receivers by merely connecting the primary winding of the-transformer Eil of any of the correction circuits to the output terminals oi' the detectors C, or CD of the receivers of Figs. l., 2, 3 and 3a, respectively. When the receivers are so modined phase modulated signals may be received thereon without distortion. l

In Fig. 11, a plurality of aerial systems, X, Y and Z may be coupled through radio frequency amplifiers X1, Y1 and Z1 to the amplifier and/or combining unit indicated diagrammatically at 2. The units X1, 'Y1 and Z1 may be heterodyne receivers which reduce the signals to an intermedivate frequency for transmission over the lines to the unit i. The unit 2 may include the radio frequency amplifiers or a heterodyne receiver in addition to the combining unit. The output of the unit is, as indicated, connected by wayoi leads 3 and 5 to a frequency or phase or amplitude modulated signal receiver 80 oi the type shown in any of the Figs. l, 2,13 and 3a.

When the unit 89 includes a frequency modulation receiver, a correction circuit. as illustrated in Figs. 6. '1, 7a, 8, 9, or 9a, may be included in the unit 8| shown dotted between the receiver t@ and the output jack in order to enable distortionless reception of phase modulated waves.

Furthermore, it will be obvious that the present invention is especially applicable to diversity receiver systems in which automatic volume control -ior the radio frequency amplifiers is provided.

Such a system then might take the form of the arrangement disclosed diagrammatically in Fig. lla. In this arrangement, a direct current component is derived from the output of the demodulation tube or rectiiler and fed back to the radio frequency amplifiers of the units X1, Y1 and Z1 where it is used to determine the biasing potential applied to the tubes therein thereby determining the amplification factor of the tubes. The arrangement is such that the desired relation between received signal strength and biasing potential may be maintained. A more complete understanding of the details ci this volume control may be had by referring to Moore U. S. Pat. #1,849,632, and Crosby U. S. Pat. #1,835,761.

Although in the arrangement of the present invention as illustrated above, in general tubes oi the triode type,except for the dynatrons of Figs. 9 and 9a are used, it will be understood that said circuits may obviously be modified touse any of the t oi tubes in general use today. For ex-I ampie. tubes of the screen grid type mav be inserted in place of the triodes illustrated without departing-trom the spirit of vthe present invention. Furthermore. other tubes also may be utilized. the only provision being that the tubes have the desired onerating characteristics.

I claim:

l. The method which includes Ysubjecting a phase modulated wave to a frequency demodulation and amplifying the higher frequencies of the demodulated waves to a lesser extent than the lower frequencies oi the demodulated waves.

2. Means ior r1 :ceiving and demodulating waves oi substantially constant amplitude the phase oi which is varied substantially in accordance with channels including signal wave phase shifting means, and a lter circuit connected to said combining means, the character of said filter circuit being such that the amplitude oi the signal in the output thereof is inversely proportional to the frequency of the signal applied to the input thereof from said combining means.

d. Means for demodulating high frequency o8 cillations modulated in phase at `signal frequency i comprising, signal collecting means,` signal combining means, a plurality of channels of different electrical length connecting said combining means to `said collecting means, the electrical length oi one of said `channels varying with the phase oi the received signal, indicating means, and a correction circuit interposed between said demodulating means `and said indicating means, said correction circuit including a frequency discriminating reactance whereby the voltages applied irom said correction circuit to said indicating means vary inversely as .the frequency of the signal components impressed from said demodulating means on the input of said correction circuit. i

5. Means for demodulating high frequency oscillations modulated in phase at signal frequency comprising, signal collecting means, signal combining means, a plurality of channels oi' dierent electrical length connecting said combining means to said collecting means, signal demodulating means coupled to said combining means, signal indicating means, and a correction circuit interposed between said demodulating means and said indicating means, said correction circuit including a thermionic tube having its input electrodes connected to said demodulating means and its output electrodes connected to said indicating A-`means by means ci ohmic resistance and reactance so related that the output voltages vary inversely as the frequency of the audio frequency signals on the input of said correction circuit.

6. In a system for amplifying and demodulating waves modulated at signal frequency, wave 6 Y aeaoaia amplifyingand amplitude limiting means, a cir.- cuit for impressing the waves to be demodulated on said means, an output circuit connected to said means, a combining circuit, a plurality of` signal transmission linesof different electrical length connected to'said output circuit, means connecting each of said lines to said combining circuit, and a rectifier connected at its input to -said combining circuit and at its output to signal 10 indicating means, and a correction circuit interposed between said rectier output and said sig- `nal indicator, said correction circuit comprising reactances which modify the amplitude of potentials passed thereby substantially in inverse proportion to their frequency. e

'7. A phase modulated signal receiver comprising, signal absorption means, signal combining means, a plurality of transmission channels connected with said absorbing means, at least one of said channels comprising a filter circuit of appreclable electrical length, which length varies as the character of the received signal varies, means for coupling points on each of said channels at which the signal waves travelling therein are of di'erent phase to said combining means, and a signal frequency discriminating circuit connected to said combining means, the character of said frequency discriminating circuit being such that it modiiies the amplitudes of the potentials passed thereby substantially in inverse proportion with respect to the frequency of said potentials passed thereby. f

8. Receiving means including the combination of signal responsive means, signal combining means, a plurality of channels of appreciable electrical length connecting said responsive means to said combining means. and a filter cir- ,cuit connected to said combining means. the

a character of said filter circuit being such that the amplitude of the signals in the output thereof is inversely proportional to the frequency of the signalsimpressed from said combining means on the input of said lter.

9. A receiving system for translating carrier waves of constant amplitude modulated in accordance with a signal to be transmitted comprising means for receiving wave energyfso modulated, means for transforming the wave energy 56 received intowaves of varying amplitude, -means for rectifying the wave energy of varying amplitude so as to produce wave energy of .modulation frequency. and means for amplifying said last mentioned wave energy an amount inversely propov-tional to the modulation frequency thereof.

10. A receiving system for translating carrier waves of constant amplitude modulated in accordance with a signal to be transmitted comprising means for receiving wave energy so modu- 60 lated, means for transforming 'the wave energy received into waves of varying amplitude, means for rectifying the wave energy of varying amplitude so as to produce wave energy of modulation frequency, and means for amplifying saidlast mentioned wave energy an amount which bears an inverse relation to the modulation frequency thereof.

11. In combination, means for picking up phase modulated Waves, a frequency modulation receiver coupled to said pick-up means for translating the phase modulated waves into waves of modulation frequencies, a correcting circuit, and means for passing said Waves of modulation frequencies through said correcting circuit, said cor" recting circuit having a characteristic such that its output variesinversely with the frequency of the input applied thereto.

12. The methodwhich includes subjecting a phase modulated wave to a frequency demodulationjand attenuating the resulting demodulated 5 waves of lower frequency to a lesser extent than the demodulated Waves of higher frequency.

13. 'I'he method of radio reception which includes receiving phase modulated high frequency carrier wave energy, subjecting the received en- 10 ergy to a frequency demodulation, and amplifying the resulting demodulated waves in such a way that the demodualted waves of lower frequency are amplied to a greater ,extent than the demodulated waves of higher frequency. 15

14. The method of radio reception which includes receiving phase modulated high frequency carrierv wave energy, heterodyning the received Waves to a convenient intermediate frequency, subjecting the waves of intermediate frequency 20 to a frequency demodulation,- and attenuating waves resulting from the said frequency demodu- 'lation in such a way that the demodulated waves of higher frequency are attenuated to a greater extent than the demodulated waves of lower fre- 25 quency.

15. The method of radio reception which includes heterodyning received phase modulated high frequency carrier waves to a convenient intermediate frequency, subjecting the waves of 30 intermediate frequency to a frequency demodulation to obtain a band of low frequency currents, and amplifying the low frequency currents of said band to a substantially greater degree than the high frequency currents thereof. 'as

16. The method of radio reception which includes receiving phase modulated wave energy. subjecting the received energy to a frequency demodulation and attenuating the higher frequencies of the demodulated waves to a greater ex-l 40 tent thanthe lower frequencies of the demodulated waves.

17. The method of radio reception which includes receiving modulated signal waves, subjecting the received waves to a frequency de- 45 modulation, and amplifying the demodulated waves in such a way that the amplification varies inversely with the frequency of the demodulated c waves.

18. -In a system for demodulating high fre- 50 quency wave energy which has its phase swung with respect to a reference phase an amount substantially proportionalv to the modulation voltage over a portion of the frequency range of the modulation voltage, means forreceiving wave '55 energy so modulated, a frequency modulation demodulation system having an input coupled to said aforesaid means and having an output, signal indicating means having an input, and a circuit, having -a characteristic such that voltages 60 of higher modulation potential frequencies are attenuated thereby an amount greater 'than voltages of lower modulation potential frequencies, coupling said frequency modulation demodulator to said signal indicating means input. -65

19. The method of demodulating wave energy of constant amplitude which has been varied in. wave length by modulating potentials modied in such a manner that the resulting wave length modulation includes phase and frequency modu- '7 lation components comprising, receiving energy so modulated, subjecting the received energy to a frequency demodulation and amplifying the resulting demodulated waves in such a way that the demodulated waves of lower signal frequency .7 5

are amplified to a greater extent than the demodulated waves of higher signal frequency.

20. The method of signalling which includes, receiving a wave which has been modulated so as to include frequency and phase modulated components, substantially eliminating amplitude changes in said wave, subjecting said wave to a frequency demodulation, and attenuating the resulting demodulated waves of lower frequency to a lesser extent than the demodulated waves of higher frequency.

21. The method which includes, subjecting a modulated wave, modulated so as to be a combined frequency and phase modulated wave, to a frequency demodulation, and attenuating waves of lower frequency resulting from the demodulation to a lesser extent than waves of higher frequency resulting from the demodulation.

22. The method of radio reception which includes, receiving high frequency carrier wave energy which Wave energy is modulated so as to include frequency and phase modulated signal components, heterodynng the received energy, substantially eliminating amplitude changes in the heterodyned energy, subjecting the heterodyned energy to a frequency demodulation and amplifying the resulting demodulated waves in such a way that the demodulated waves of lower frequency are amplified to a greater-.extent than the demodulated waves of higher frequency.

MURRAY G. CROSBY. 

